Abstract
Traditionally, there has been a trade-off in spectroscopic measurements between high resolution, broadband coverage, and acquisition time. Originally envisioned for precision spectroscopy of the hydrogen atom in the ultraviolet, optical frequency combs are now commonly used for probing molecular ro-vibrational transitions throughout broad spectral bands in the mid-infrared providing superior resolution, speed, and the capability of referencing to the primary frequency standards. Here we demonstrate the acquisition of 2.5 million spectral data points over the continuous wavelength range of 3.17–5.13 µm (frequency span 1200 cm−1, sampling point spacing 13–21 MHz), via interleaving comb-tooth-resolved spectra acquired with a highly-coherent broadband dual-frequency-comb system based on optical subharmonic generation. With the original comb-line spacing of 115 MHz, overlaying eight spectra with gradually shifted comb lines we fully resolve the amplitude and phase spectra of molecules with narrow Doppler lines, such as carbon disulfide (CS2) and its three isotopologues.
Highlights
There has been a trade-off in spectroscopic measurements between high resolution, broadband coverage, and acquisition time
When one of the comb teeth is phase locked to a narrow-linewidth reference laser(s), frequency comb spectroscopy can provide the spectral resolution, which is on par with tunable laser spectroscopy—limited only by the absolute comb-tooth linewidth
Using quantum cascade laser (QCL) combs, Villares et al performed dual comb spectroscopy (DCS) measurements near 7 μm with the sampling point spacing that was improved from the original comb-tooth spacing of 7.5 GHz to 80 MHz by frequency sweeping the combs via QCL current modulation[15]
Summary
There has been a trade-off in spectroscopic measurements between high resolution, broadband coverage, and acquisition time. We demonstrate the acquisition of 2.5 million spectral data points over the continuous wavelength range of 3.17–5.13 μm (frequency span 1200 cm−1, sampling point spacing 13–21 MHz), via interleaving comb-tooth-resolved spectra acquired with a highly-coherent broadband dual-frequencycomb system based on optical subharmonic generation. In the mid-IR, Baumann et al used difference frequency combs near 3.4 μm (spectral span 30 cm−1), to attain a high-resolution spectrum of methane, by interleaving spectra acquired by shifting the combs by 25 MHz—one-quarter of the 100-MHz comb-tooth s pacing[10]. Using quantum cascade laser (QCL) combs, Villares et al performed DCS measurements near 7 μm (span 16 cm−1) with the sampling point spacing that was improved from the original comb-tooth spacing of 7.5 GHz to 80 MHz by frequency sweeping the combs via QCL current modulation[15]. The comb lines were scanned over 16 GHz—a small portion of the 127-GHz mode s pacing[18]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
